April 21, 2014

Astro Event: The Closest Full Moon of the Year.

Last year's Wolf Moon as seen from Astroguyz HQ in Hudson, Florida. (Photo by author).

Last year's Wolf Moon as seen from Astroguyz HQ in Hudson, Florida. (Photo by author).

(Editorís note: Due to a flurry of astronomical events, Februaryís events of the week will be released on an accelerated schedule; hang on!)

Amid the opposition of Mars, two launches out of the KSC and the Cape next week, and an exceptionally fine elongation of Mercury in the early morning skies, this weekend brings us a special treat; the closest Full Moon of the year. This Moon, known also as the Full Wolf Moon, is technically full at precisely 06:00 Universal time on Saturday morning, the 30th of January. This comes only 3 hours prior to perigee, when the Moon is closest to Earth in its orbit. At this time, the Moon will be only 217,862 miles distant, and appear 34.1í arc minutes in size, as opposed to 29.3í arc minutes at apogee. An added plus is that this Full Moon occurs at a very northerly declination in the constellation Cancer, and hence will be riding high for northern hemisphere viewers all night. And donít forget ruddy Mars, just 7į degrees north of the Moon!

The astro word for this week is albedo. Think that bright silvery Full Moon is bright? Science says otherwise. Albedo is the measure of the percentage of light reflected back by an astronomical object; 100% is a full mirror, optimal reflection, and 0% is pitch black. On Earth, fresh snow reflects about 85% of the light that falls on it, and the average albedo of Earth is about 30%, depending on the amount of cloud cover and the percentage of land versus ocean presented to the Sun. In fact, this phenomenon of reflectivity may play a key role in a lesser known effect impacting global climate; that of global dimming. Now for the real shocker; the average albedo for the Moon is about 10%, slightly less than worn asphalt! Ask the Apollo astronauts; the Moon is in fact, a very grey-to-black place! The reason that this weekendís Full Moon looks bright is that you are seeing the sum of 5% of the Sunís reflected light crammed into an area tinier than a fingernail at armís length. In fact, anyone who has stood under a 99% percent eclipsed Sun, as occurred earlier this month, will tell you that even 1% of the sunís output is still pretty bright!